Shiliew is not supposed to earn the title of WSS. He's a backstabbing little shit with no honor. Which is exactly how he will defeat Mihawk and get the title of WSS, thus rendering it meaningless. That's the entire premise of the BBPs. They are not your average crew, they metagame. They cheat and plan for decades and only fight when they know they can win.
If Luffy has the Heart of the Cards on his side, BB has a thousand Uno Reverse Cards up his sleeve.